This exceptionally rare and important precision chronometer, or deck watch, was crafted by the famed Vacheron Constantin. One of the most accurate instruments ever created for measuring time, the precision instrument's primary function was to determine longitude at sea using celestial navigation. With the timepiece, which was set to Greenwich Mean Time, one could accurately calculate a ship's longitude by referencing the time the sun or a star crossed the ship's meridian.

Specially crafted to be kept on a ship’s deck for quick reference, this “Heure exacte” watch was able to keep time even in the roughest waters. Housed in a three-part mahogany deck box, this timepiece is accompanied by letters of certification from Vacheron Constantin.

Crafted in 1929

Case: 4 1/2” wide x 5 3/4” deep x 2 3/4” high

The Geneva firm of Vacheron Constantin was founded in 1755 by horologist Jean-Marc Vacheron, and is the oldest watch-making firm with a continuous history. Through its many innovations in both the science and design of fine timepieces, the firm has garnered numerous awards, and the attention of international heads of state and royalty, including Dwight D. Eisenhower and King Farouk of Egypt. Today, Vacheron Constantin is arguably the oldest watch-making firm in continuous operation since its inception over 250 years ago. Today, the company holds the record for creating the most expensive wristwatch, the Kallista, in 1979, and the most complicated, the Tour de I'Ille, crafted in 2005 of 16 complications comprised of 834 component parts.

Reference:
Collector’s Dictionary of Clocks and Watches, 1999, Eric Bruton